Experimental study on the efficiency of different substances in retarding the absorption of penicillin introduced into the subconjunctival spaces.

THERE is no doubt that therapeutic levels of penicillin can be obtained in the aqueous and the tissues of the anterior segment of the globe, by injecting correct doses of the antibiotic subconjunctivally. Such levels are slightly higher than those reached with equal doses by systemic administration (Sorsby and Ungar, 1946-48; Andrews, 1947). The degree of impurity shown by the first preparations of the antibiotic did not permit the quantity of penicillin introduced at each injection to exceed 10,000 to 20,000 units dissolved in 0.5 ml. distilled water. The high degree of purity obtainable at the present time, and the perfect solubility of the substance, now permit the introduction of 500,000 to 1,000,000 units dissolved in 0`5 ml. distilled water, preceded by a simple cocaine anaesthesia. These large doses admit the advantage of reaching the highest concentration in the aqueous and ocular tissues, but do not prevent the rapid elimination -of the substance from the subconjunctival area backward through the lymphatic epibulbar spaces. This constitutes d great obstacle to the common use of the drug in subconjunctival injections, on account -of the frequency with which the injections must be administered. Some substances have recently been tested to discover an agent which, when injectedc locally with penicillin, will to Isome degree retard its absorption. In order to determine the degree to which such substances can retard the absorption of penicillin, we have carried out research, under various conditions, into the rhythm with which the drug passes into the aqueous, together with the blood level. In a series of experiments on rabbits, we tested the efficiency of several associations as follows: